First up, I think your question is less something for crypto.SE and would fit better in the security.SE corner. Nevertheless, here goes:
...except his name or identity...
That's in itself already describes your problems when it comes to security and cryptography.
Problem due to lack of verification options.
Currently, world news outlets (example: Reuters) as well as US governments confirm that Mr. Snowden's passport has been revoked by the US government. As a result, you don't have the option to verify if the person you are talking to is indeed Mr. Snowden, as there are no official documents that could indeed verify the identify in a trustworthy way.
Problem due to lack of knowledge.
As you have never met Mr. Snowden in person either, you can't tell if a person you meet is indeed Mr. Snowden and not someone who looks “just like him”. Remember that the only "knowledge" you currently have is a name and a small pack of pictures posted by news outlets. Keeping it short: since you both have no "common knowledge" which could be used to establish "trust", you can not trust the person you talk to.
Now... security is based on knowing, doing, or owning something that no one else can. This is especially true when thinking about cryptography for communication purposes. Since you don't even know Mr. Snowden and he does not know you, there is no way to establish a secure connection and/or communication.
In fact, you both represent "untrusted endpoints" for each other. You can't establish a secure connection when one or more endpoints are untrusted. To give you an every-day example: that's like trusting an invalid certificate when visiting an SSL protected website.
Keeping it short: symmetric key cryptography is not an option.
The alternative would be using public key cryptography instead. BUT: to avoid that everyone can decrypt the message, the decryption key would need to be passed to Mr. Snowden confidentially instead of publically... which does not satisfy the definition of "public key cryptography" anymore. Also, you can not establish a secure connection to an untrusted endpoint which means you can't securely pass the decription key. This practically closes the loop.
Wrapping it up: Humans are often the weakest link in a security protocol. This is one of such cases.
EDIT
Recently found a cartoon which provides asome nice, reality-checking perspectiveperspectives on the discussiondiscussions that came up in the comments to my reply...
- Can you trust a “public video”?
![enter image description here](https://i.sstatic.net/UJUyS.png)
![Council of 300](https://i.sstatic.net/RyiKd.png)
- Even if you can trust the public video to transport a key, and even when you ignore the endpoint you can't verify with certainty... the “trust problem” remains due to “untrusted transport channels”. As said: in this case humans are the weakest link when trying to find a secure way of doing this.
![crypto nerd](https://i.sstatic.net/UJUyS.png)
(viaimages via http://xkcd.com/538/http://xkcd.com/, licensed CC BY-NC 2.5)